Embodiments herein generally relate to electrostatic printers and copiers or reproduction machines, and more particularly, concern a vacuum belt used within a printing device that has an irregular pattern of holes.
Direct-to-paper printing architectures require precise and robust media handling, particularly for applications where the proximity of the printhead(s) necessitates that the media is flat everywhere, including the edges, to avoid damaging the printhead(s). In view of this, a vacuum transport system is presented which uses a belt with a non-uniform hole pattern and an alignment unit that places the media onto specific locations on the vacuum belt. With this approach, unlike conventional vacuum transport systems, it is possible to capture and hold flat media whose edges are creased or curled (above a certain limit of creasing or curling).
More specifically, embodiments herein comprise a printing apparatus that includes a printing engine (e.g., an electrostatic and xerographic printing engine) and a media path. The media path transports sheets of print media relative to the printing engine. Further, the printer includes a vacuum belt within the media path and a vacuum plenum adjacent the vacuum belt. Embodiments herein can also include an alignment unit within the media path.
The vacuum belt has belt edges and a contact surface between the belt edges. The contact surface contacts sheets of print media. The sheets of print media have sheet edges (e.g., usually 4, for rectangular sheets) and a central sheet region.
The contact surface of the vacuum belt has a central belt region located where the central sheet region of the sheets of print media contacts the contact surface of the vacuum belt. Also, the contact surface has border regions located where the sheet edges of the sheets of print media contact the contact surface of the vacuum belt. The central belt region is located between (and can be surrounded by) the border regions. For example, the border regions can comprise one or more rectangles of differing sizes, which may or may not be nested within each other.
The contact surface has vacuum holes and the vacuum plenum draws air in through the vacuum holes. The vacuum holes comprise an irregular (non-uniform) pattern, because a different density of holes is located within the border regions relative to the central belt region. For example, the density of the vacuum holes can be higher in the border regions relative to the central belt region and/or the vacuum holes can be smaller or larger in the border regions relative to the central belt region
The alignment unit can adjust the position of the sheets in a two-dimensional space (X-Y coordinates) within the sheet path relative to the position and timing of the contact surface such that the sheet edges of the sheets of print media are positioned on the border regions of the contact surface as the sheets are moved by the vacuum belt.
These and other features are described in, or are apparent from, the following detailed description.